Coccidioides posadasii and Coccidioides immitis are both filamentous fungi and the causative agents of coccidioidomycosis, commonly known as Valley Fever. Over the past several decades, valley fever cases have increased dramatically, and the endemic range has expanded with recent verification of the organism in soil in Eastern Washington. These fungi are primary pathogens that can be responsible for morbidity and mortality in otherwise healthy patients, and disease can vary from asymptomatic to lethal. The underlying reasons for disease variation, and the role fungal genotype plays, represents a major gap in our knowledge. Our overall knowledge of the biology of Coccidioides is limited. The proposed project will define an entirely new life cycle stage, with high impact both for disease as well as understanding evolutionary potential. The existence of an ascospore that could be infectious, and have differential infection dynamics would explain at least in part, disease variation in human patients. Ascospores are also often resting structures in the environment that may provide environmental refugia for the fungus. Finally, recombined offspring may have novel phenoytpes that can adapt to new hosts and environments. The project will use standard mycological media and techniques to validate our preliminary results. Our approach will be focused on using genomic sequencing to define recombination patterns and frequency. Gaining an understanding of the mechanism of recombination, and potential new infectious spore type could greatly affect how disease prevalence and complications are viewed. This strategy will elucidate differences among recombinant Coccidioides strains for phenotypes such as stress tolerance, antifungal resistance, and pathogenicity, and determine if this is a mechanism of disease variation. The outcomes will fundamentally change our understanding of Coccidioides biology. The knowledge gained will allow for new genetic and mechanistic studies of Coccidioides.